Colloquium (2017)

ASIAA Colloquium is usually held on Wednesdays at 2:20-3:20 pm in Room 1203 of the Astronomy-Mathematics Building, NTU. All scientists are welcome to attend.

The ASIAA-NTU joint colloquium series aims to bring to the physics/astronomy/cosmology community in ASIAA/NTU world renown researchers who will talk about the forefront development of physical sciences.

To understand the properties and evolution of protoplanetary disks, ALMA surveys on protoplanetary disks have been conducted toward several star-forming regions. In these surveys, several tens of disks have been imaged in dust continuum, providing detailed information of dusty disks of a large sample. However, the gas distributions and velocity structures of most of the disks can still not be imaged at high S/N ratios because of the short integration time per source in these surveys. In this presentation, I will introduce our project to extract more information from molecular-line data of these ALMA surveys and to study disk properties traced by molecular lines with the velocity-aligned stacking method. I will discuss the relation between gas and dust masses in protoplanetary disks and dynamically and spectroscopically determined stellar masses. I will also introduce our next project aiming to measure dynamical stellar mass of a large sample.

2

2017-12-27 Wed14:20~15:20R1203

Yi-Kuan Chiang[JHU]

Which Galactic dust map should I use? Insights from extragalactic tomography

Abstract

Over the past few years, clustering-based redshift estimation has emerged as a new way to estimate redshifts and perform extragalactic tomography of arbitrary datasets. On a similar timescale, observations by Planck, WISE, Pan-STARRS and 21cm radio surveys have been used to create a multitude of SFD-type Galactic dust maps. I will explain how clustering-based redshift estimation can be used to test the quality of the seven different dust maps currently available and I will show that extragalactic signatures can be revealed in many of them. When such maps are used for correcting optical magnitudes, we therefore expect biases which are likely to affect the precision of cosmological experiments using supernovae, BAOs, or the growth of structures. I will present possible solutions to alleviate this issue and discuss which map should be used depending on which measurement one wishes to make.

The big number of spectra collected nowadays by large spectroscopic
surveys (such as LAMOST, APOGEE, RAVE, and others) requires software
for automated analysis. I present the software SP_Ace, designed to
derive stellar parameters and chemical abundances. I describe how it
works and show its performance with application on real spectra such
as the ELODIE spectral library and the LAMOST database, with which we
recently performed the analysis of the LAMOST spectra of the first
data release (DR1, paper submitted). I also discuss some key points
that affect the accuracy of any method of spectroscopic analysis.

4

2017-12-18 Mon14:20~15:20R1203

Derek Fox[Penn State]

*Special Seminar*Seeking the Sources of IceCube's Cosmic Neutrinos

Abstract

The IceCube Collaboration has reported their discovery of high-energy
(e_nu > 1 TeV) neutrinos of cosmic origin. Since the original
announcement in 2013, the confidence level of their discovery has
increased to >5-sigma, and the signature of this relatively
hard-spectrum, isotropic or near-isotropic population of neutrinos has
been recovered via multiple event selections. Despite increasingly
energetic efforts, however, no high-confidence source has been
identified for any of the high-energy neutrinos. At Penn State, the
Astrophysical Multimessenger Observatory Network (AMON) has been
pursuing and enabling time-sensitive searches for neutrino
counterparts which might reveal these sources. I will discuss our
efforts, which have included archival analyses, rapid-response X-ray
and UV/optical observations with NASA's Swift satellite, and recently,
multiwavelength studies of a particularly interesting BL Lac-type
blazar, TXS 0506+056. Whatever the nature of the sources emitting
IceCube's cosmic neutrinos, they are some of the universe's
highest-energy particle accelerators, and may also be the long-sought
sources of the highest-energy cosmic rays.

5

2017-12-14 Thu14:20~15:20R1203

Juliana Kwan[Kavli IPMU]

*Special Seminar*Cosmology from joint probes of clustering and weak lensing

Abstract

We live in an exciting time for cosmology. With ongoing imaging surveys such as Dark Energy Survey (DES) and the Hyper Suprime-Cam (HSC) Survey covering increasing volumes of sky, we are now able to explore much more of the large scale dark matter distribution with weak gravitational lensing. Observations of galaxy-galaxy lensing and cosmic shear provide new information on the nature of dark energy and cosmic acceleration by breaking cosmological parameter degeneracies when combined with galaxy clustering. However, the sophistication of our theoretical modelling needs to match the precision of our observations. This will be especially significant for small deviations to the standard model such as massive neutrinos and time variations to the equation of state parameter for dark energy.
This talk presents results from one of the first studies from DES involving joint probes of weak lensing and large scale structure. I will also talk about the analysis tools that I have built to supply percent level predictions for highly non-linear quantities such as the halo bias and mass function using a large suite of N-body simulations including dynamical dark energy and massive neutrinos.

Protoplanetary disks of gas and dust encountered around low and intermediate young stars are now recognized as sites of planet formation. Determining as accurately as possible their physical parameters, such as the temperature and the density, is therefore fundamental. So far, our knowledge of these physical parameters remains in many cases model dependent. In the first part of this seminar, I will discuss some recent results we have obtained using ALMA and NOEMA to study the TW Hydra and the Flying Saucer protoplanetary disks. I will then briefly discuss disk evolution by showing the results of the survey of hybrid disks we have done using the IRAM 30-m telescope and APEX.

Gas-rich star-forming galaxies are the main contributors to the buildup of stellar and black holes masses in the Universe, which took place rapidly between the redshift of z=1-3. Both star formation and active galactic nucleus (AGN) activity are related to the gas content and the dynamics of their host galaxies, which in turn shape their subsequent evolution to the present epoch. In this talk, I will present our recent findings in characterizing the interstellar medium (ISM) of dusty star-forming galaxies (DSFG) and powerful quasars using multi-wavelength photometry and CO- and [CII]- line imaging obtained with telescopes such as ALMA, VLA, PdBI, and SMA. In particular, I will focus on our findings of the most massive z~3 "main-sequence" disk galaxy discovered in the rare sample of IR-luminous galaxies at the peak epoch of cosmic star formation using the Herschel Space Observatory. I will conclude with a discussion on the implications of these studies in the context of galaxy formation and evolution.

8

2017-12-06 Wed14:20~15:20R1203

Michael Ireland[ANU]

Answering fundamental questions of exoplanet formation and habitability with new facilities

Abstract

The question “how do planets form and evolve?” remains complex and difficult to answer, as current telescopes including ALMA, as well as the coming extremely large telescopes, lack the angular resolution to distinguish between formation pathways. To properly resolve planet formation and distinguish between models, we will need to resolve scales as small as the Hill sphere, requiring an interferometer. I will describe a baseline design for the Planet Formation Imager (PFI), and how a nulling interferometer on the VLTI is an important first step in realising the goal of this facility. Answering the other big exoplanet question: “has life evolved elsewhere?” requires probes of the atmospheres of terrestrial planets. I will describe the technique of high dispersion coronagraphy (the “Siren” concept), and how measuring the reflected light spectrum of a habitable zone planet may be possible even with 8-10m class telescopes. I will outline the key technical challenges in achieving this goal - namely high end to end throughput (which has proved difficult with a prototype on Subaru) and predictive multi-wavefront sensor wavefront control for adaptive optics.

The theory of spiral density waves had its origin approximately six decades ago in an attempt to reconcile the winding dilemma of material spiral arms in flattened disk galaxies. Our review begins with the earliest calculations of linear and nonlinear spiral density waves in disk galaxies, in which the hypothesis of quasi-stationary spiral structure (QSSS) plays a central role. The earliest success was the prediction of the nonlinear compression of the interstellar medium and its embedded magnetic field; the earliest failure, seemingly, was not detecting color gradients associated with the migration of OB stars whose formation is triggered downstream from the spiral shock front. The reasons for this apparent failure are understood with an update on the current status of the problem of OB star formation, including its relationship to the feathering substructure of galactic spiral arms. Infrared images can show two-armed, grand design spirals, even when the optical and UV images show flocculent structures. We suggest how the nonlinear response of the interstellar gas, coupled with overlapping subharmonic resonances, might introduce chaotic behavior in the dynamics of the interstellar medium and Population I objects, even though the underlying forces to which they are subject are regular.
We then move to a discussion of resonantly forced spiral density waves in a planetary ring and their relationship to the ideas of disk truncation, and the shepherding of narrow rings by satellites orbiting nearby. The back reaction of the rings on the satellites led to the prediction of planet migration in protoplanetary disks, which has had widespread application in the exploding data sets concerning hot Jupiters and extrasolar planetary systems. We then return to the issue of global normal modes in the stellar disk of spiral galaxies and its relationship to the QSSS hypothesis, where the central theoretical concepts involve waves with negative and positive surface densities of energy and angular momentum in the regions interior and exterior, respectively, to the corotation circle; the consequent transmission and overreflection of propagating spiral density waves incident on the corotation circle; and the role of feedback from the central regions.
Lastly, we discuss how the amplitude modulation predicted for the destructive interference of oppositely propagating waves that form standing wave patterns may have been observed in deep infrared images of nearby spiral galaxies. We also present without comment the tantalizing ALMA image of spiral structure in the protoplanetary disk around the forming star Elias 2-27.

10

2017-12-04 Mon14:20~15:20R1203

Kyle Parfrey[Berkeley]

*Special Seminar*Relativistic Accretion onto Neutron Stars

Abstract

Accreting neutron stars produce a wide range of astrophysical phenomena including X-ray binaries, ultra-luminous X-ray sources (ULXs), and potentially short- and long-duration gamma-ray bursts. There are several long-standing puzzles, such as the cause of millisecond pulsars’ limiting spin frequency and the mechanism underlying their relativistic jets, as well as recent problems raised by the newly discovered transitional millisecond pulsars and the pulsing ULXs. I will present results from the first relativistic MHD simulations of accretion onto magnetized, rotating neutron stars, performed in general relativity in the Kerr spacetime geometry. Four distinct states of the magnetosphere-disk system are found, depending on the stellar field strength and the mass accretion rate. A Poynting-flux-dominated relativistic jet, powered by stellar rotation, is produced at high accretion rates. The simulations suggest that rapidly rotating neutron stars with a magnetar-strength fields may be responsible for short gamma-ray bursts, including the neutron-star merger event GW170817.

11

2017-11-27 Mon14:20~15:20R1203

Nadia M. Murillo[Leiden Observatory]

*Special Seminar*Forming stellar siblings: a look at the chemistry and physics of multiple stars

Abstract

Multiple stars are commonly found throughout our galaxy at all mass ranges. They are excellent stellar physics laboratories and the cause of many interesting phenomena such as certain types of supernovae, planetary nebulae and binary black holes.
Observations find multiplicity at all stages of stellar evolution. An elevated frequency of multiplicity is found at the early stages of star formation, which shows that most stars are formed in multiple systems. In this talk we look at some of the open questions regarding formation and structure of multiple stars, namely the formation of rotationally supported disks, chemical structure of early stage star formation, and the factors that influence star formation. Multi-wavelength observations are coupled with chemical and physical models, to address these questions. We demonstrate that stellar multiplicity is common and needs to be taken into account in our picture of star formation.

12

2017-11-22 Wed14:20~15:20R1203

Kate Su[University of Arizona]

*Special Seminar*Baby Photos of a Scaled-Up Solar System - HD 95086

Abstract

Planets and minor bodies such as asteroids, Kuiper-belt objects and comets are integral components of a planetary system. Interactions among them leave clues about the formation process of a planetary system. The signature of such interactions is most prominent through observations of its debris disk at millimeter wavelengths where emission is dominated by the population of large grains that stay close to their parent bodies. I will discuss our ALMA 1.3 mm observation of HD 95086, a young early-type star that hosts a directly imaged giant planet b and a massive debris disk with both asteroid- and Kuiper-belt analogs. The high angular resolution and sensitivity provided by ALMA enable us to resolve the Kuiper-belt analog for the first time. Based on the disk properties, HD 95086 is truly a young analog of HR 8799, suggesting a common path on how planetary systems form and evolve.

13

2017-11-21 Tue14:20~15:20R1203

Bernhard Brandl[Leiden University]

Science and Technology of the Mid-Infrared Imager and Spectrograph (METIS) at ESO's Extremely Large Telescope (ELT)

Abstract

With a collecting area of 39m in diameter, the European Extremely Large Telescope (ELT) will be the largest telescope optical/IR for many years to come. The work on telescope and instruments is in full steam, leading to expected first light in 2024. The ELT will be equipped with three scientific instruments, one of them being the Mid-Infrared Imager and Spectrograph (METIS). In this talk I present an overview of the ELT project, explain the design and science goals of METIS, and discuss some of the challenges to instruments on the next generation of extremely large telescopes.

14

2017-11-15 Wed14:20~15:20R1203

Iain Mcdonald[University of Manchester]

The fate of stars: stellar death and new life

Abstract

We are stardust, made from the insides of stars. To understand where we come from, we need to understand how material made in the cores of stars is released into the interstellar medium. A key factor in this is the timing of stellar mass loss. In this talk, I will argue that the mass-loss formulisms we currently use for low-mass stars are not fit for purpose, and that a new one needs to be constructed. I'll discuss the work we are doing to calibrate the mass-loss prescription for evolved stars, particularly in the early Universe, where the mechanisms of stellar mass are not well calibrated.

Current large-scale cosmological simulations began to reproduce realistic galaxy populations, where strong galactic outflows driven by supernovae have been identified as one of the key ingredients to this success. However, the origin of galactic outflows remains poorly understood, and the phenomenological recipes of outflows adopted in cosmological simulations render their predictive power somewhat ambiguous. In this talk, I will argue that the way to move forward is to utilize high-resolution simulations of galaxies in an idealized setup where supernova feedback and the multi-phase interstellar medium can be properly resolved. I will show that converged outflow properties can be obtained at the resolution of ~ 5 solar masses. Outflows are driven by the hot and over-pressurized gas which breaks the disk during the formation of superbubbles. Injecting the terminal momentum of individual supernova blastwaves, a common remedy adopted in the literature to compensate unresolved supernova events, fails to drive outflows due to its incapability to thermalize the gas.

16

2017-11-09 Thu14:20~15:20R1203

Prajval Shastri[Indian Institute of Astrophysics]

AGN Circum-nuclear Environments at z~0

Abstract

The well-established scaling relationships for supermassive black holes can be preserved across cosmic time if star formation in these galaxies is regulated by feedback via mechanical and radiative power from the accreting central supermassive black hole. We have undertaken a multi-wavelength investigation of about 130 southern AGN at redshifts<0.02, in order to search for signatures of AGN feedback. We have obtained optical integrated field unit datacubes for our sample with the Siding Spring 2.3m telescope, and are doing follow-up radio imaging with the GMRT and ATCA in addition to the compilation of data at multiple frequencies. Our work in progress on this multi-wavelength investigation will be discussed.

17

2017-11-01 Wed14:20~15:20R1203

Po-Chieh Yu[NCU]

The Story of GW170817/EM170817

Abstract

On August 17, 2017 at 12∶41:04 UTC, the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their fifth observation of gravitational wave (GW), GW170817. For the first time, astronomers confirmed the electromagnetic (EM) counterpart of GW170817 in the nearby galaxy NGC 4993, is due to a binary neutron star merger. Since neutron stars merger is the candidate site for nuclear synthesis of heavy elements such as gold, the work of global network can help in understanding the origin of the these heavy elements – one of the mystery in modern astrophysics. In this talk, I will review current results from GW170817/EM170817. Particularly, I will introduce the contribution of IANCU in this breakthrough discovery. Also, I will show the current status of Lulin observatory from follow-up observations of GW and transient sources. Finally, I will introduce several projects of IANCU and discuss what role Taiwan can play in the era of multi-messenger astronomy.

18

2017-11-01 Wed15:40~16:40R1203

Meng-Ru Wu[ASIOP]

The Gold mine of the universe: the r-process nucleosynthesis in explosive astrophysical events

Abstract

The astrophysical site hosting the formation of elements heavier than iron, including Silver and Gold via the rapid neutron-capture process (r-process) has been debated for many decades. Over the past few years, owing to the advances of theoretical development and various observational hints, the prevalent paradigm shifted largely from core-collapse supernovae to the merger of compact objects -- binary neutron stars or one neutron star with one black hole. In this talk, I will first introduce the basic concept and ingredients of the r-process nucleosynthesis. I will then discuss some of the recent evidences and discoveries which are relevant for identifying the r-process sites, including the most recent detection of the merger of the binary neutron stars. I will also speak about the theoretical uncertainties and challenges lying ahead.

19

2017-10-25 Wed14:20~15:20R1203

Yusei Koyama[Subaru Telescope]

Tracking down the evolution of cluster galaxies across cosmic time with Subaru panoramic H-alpha imaging survey

Abstract

We present our systematic, wide-field, narrow-band H-alpha imaging campaign of distant (proto-)clusters at 0.4 < z < 2.5 with Suprime-Cam, MOIRCS, and Hyper Suprime-Cam on the Subaru Telescope. Using the large H-alpha galaxies selected from a variety of environment across cosmic time, we discuss the environmental dependence/independence of various galaxy properties such as color, mass, and (specific) SFR of star-forming cluster galaxies. We also talk about our recent efforts to study environmental impacts on dust and/or molecular gas properties in galaxies using AKARI and Nobeyama 45m radio telescope. Finally, we also introduce our “ULTIMATE-Subaru” project - the next-generation, wide-field ground-layer adaptive optics (GLAO) development project of Subaru - which will become a major facility instrument of Subaru in mid-2020s after HSC and PFS.

20

2017-10-19 Thu14:20~15:20R1203

Sergei A. Levshakov[A. F. Ioffe Physical-Technical Institute]

*Special Seminar*Probing the fundamental constants of nature over cosmological time-scales

Abstract

The measurements of the fundamental constants of nature - the fine structure constant, alpha, and the electron-to-proton mass ratio, mu - using astronomical spectra of atoms and molecules are reviewed. The current results obtained from observations of dark clouds in the Milky Way, HII zones in the neighbouring galaxy M33, and high-redshift galaxies at z ~ 6 are summarized. Prospects for future observations are discussed.

21

2017-10-17 Tue14:20~15:20R1203

Neal Turner[NASA/JPL]

Starlight Reshapes Planetary Nurseries

Abstract

Many protostellar disks show central cavities, rings or spiral arms
likely caused by low-mass stellar or planetary companions, yet few
such features are conclusively tied to bodies embedded in the disks.
Even small features on the disk's surface cast shadows, because the
starlight grazes the surface. We therefore focus on accurately
computing the disk's thickness, which depends on its temperature. We
present models with temperatures set by the balance between starlight
heating and radiative cooling, and that are in vertical hydrostatic
equilibrium. The planet has 20, 100, or 1000 Earth masses, ranging
from barely enough to perturb the disk significantly, to clearing a
deep tidal gap. The hydrostatic balance strikingly alters the model
disk's appearance. The planet-carved gap's outer wall puffs up under
starlight heating, throwing a shadow across the disk beyond. The
shadow appears in scattered light as a dark ring that could be
mistaken for a gap opened by another planet. The surface brightness
contrast between outer wall and shadow for the 100-Earth-mass planet
is almost an order of magnitude greater than a model neglecting the
temperature disturbances. The shadow is so deep it largely hides the
planet-launched spiral wave's outer arm. Temperature gradients are
such that outer low-mass planets undergoing orbital migration will
converge within the shadow. Furthermore, the temperature
perturbations affect the shape, size and contrast of features at
millimeter and centimeter wavelengths. Thus, starlight heating and
radiative cooling are key factors in the appearance of protostellar
disks with embedded planets.

22

2017-10-12 Thu14:20~15:20R1203

Yen-Chen Pan[UCSC]

*Special Seminar*Understanding Type Ia Supernova with UV Spectroscopy

Abstract

Type Ia Supernovae are exceptionally bright explosions, and their calibrateable brightness makes them critical tools for probing the cosmic expansion. However, their progenitors remain unclear, which could introduce uncertainties in their use in cosmology. Theory suggests that SN Ia progenitor metallicity is correlated with its peak luminosity, but not its light-curve shape. As a result, this effect should lead to an increased Hubble scatter, reducing the precision in distance measurement. Models also indicate that changing the progenitor metallicity will have little effect on the appearance of optical SN data, but significantly change UV spectra. We obtained the sample of SN Ia with UV spectral time series from both Hubble Space Telescope (HST) and Swift satellite. The initial results are presented by comparing the SN and UV spectral features and analyse the dependence of SN properties on metallicity.

23

2017-10-11 Wed14:20~15:20R1203

I-Non Chiu[ASIAA]

Studying Cosmology with Galaxy Clusters

Abstract

Galaxy clusters contain rich information of cosmology and astrophysics. In the past, cluster science was limited by a lack of adequately deep observations in multi-wavelength and was subject to heterogeneous samples with small sizes at low redshift. The situation has been changed due to the recent success of the large mm wavelength surveys—such as the South Pole Telescope (SPT)—that employ the Sunyaev-Zel’dovich Effect (SZE) to identify and study galaxy clusters in their abundance out to the early and distant Universe. Together with the breakthroughs in the area of wide-and-deep optical and NIR surveys, such as the Dark Energy Survey and the Hyper Suprime-Cam survey, we are able to uniformly study these SZE selected samples. In this talk, I will talk about the recent results from the SPT collaboration with emphasis on various observable to mass scaling relations. I will present the unprecedented study of the baryon content of an approximately mass-limited sample of 91 galaxy clusters out to redshift 1.3. I will demonstrate the crucial need for the accurate mass calibration in order to pave a way for cluster science in the future.

24

2017-10-05 Thu14:20~15:20R1203

Sun Kwok[Univ. of Hong Kong]

Organic Matter in the Universe: from solar system to distant galaxies

Abstract

Recent observational and experimental evidence for the presence of complex organics in space is reviewed. Remote astronomical observations have detected ~200 gas-phase molecules through their rotational and vibrational transitions. Many classes of organic molecules are represented in this list, including some precursors to biological molecules. A number of unidentified spectral phenomena observed in the interstellar medium are likely to have originated from complex organics. The observation of these features in distant galaxies suggests that organic synthesis had already taken place during the early epochs of the Universe.
In the Solar System, almost all biologically relevant molecules can be found in the soluble component of carbonaceous meteorites. Complex organics of mixed aromatic and aliphatic structures are present in the insoluble component of meteorites. Hydrocarbons cover much of the surface of the planetary satellite Titan and complex organics are found in comets and interplanetary dust particles. The possibility that the early Solar System, or even the early Earth, have been enriched by interstellar organics is discussed.

25

2017-09-27 Wed14:20~15:20R1203

Zan Peeters[ASIAA]

The Academia Sinia nanoSIMS lab 2013--2017: an overview

Abstract

As I am about to leave ASIAA I want to give a summary of the achievements of the nanoSIMS lab over the past four years. I will discuss results regarding my own topic, the organic matter found in meteorites, and its relation to the formation of the Solar System. I will also highlight the results of collaborations with other scientists, which includes a search for presolar grains in meteorites, and non-astronomy experiments such as heavy metals in rice roots and oxygen isotopes in fish.

26

2017-09-22 Fri14:20~15:20R1203

Yuan-Sen Ting[Princeton/IAS]

*Special Seminar*Neural networks and their applications in physical sciences

Abstract

Neural networks have gained much attentions in recent years due to their applications in various daily aspects including facial/voice recognition and data mining. Despite their remarkable ability, neural networks are severely underutilized and have not realized its full potential in physical sciences. In this talk, I will briefly explain the basic concepts as well as some exciting frontier ideas in neural networks. I will discuss the opportunities of applying this simple yet interesting idea to physical sciences using my studies of the Milky Way as an example. In particular, I will describe how a combination of data-driven models and neural networks can be an effective tool to harness information from low-resolution spectra and to relate various fields in physical sciences -- such as the studies of spectroscopy and asteroseismology in astronomy.

27

2017-09-21 Thu14:20~15:20R1203

Yuan-Sen Ting[Princeton/IAS]

*Special Seminar*The new era of Galactic Archaeology

Abstract

Understanding physical processes responsible for the formation and evolution of galaxies like the Milky Way is a fundamental problem in astrophysics. However, a key challenge is that the properties and orbits of the stars can only be observed at present: to understand what happened in the Milky Way at earlier epochs, one must explore “archaeological” techniques. One idea, "chemical tagging,” aims to probe the history of the Milky Way via the unique imprint in chemical abundance space of long-disrupted star forming associations. I will discuss the opportunities and challenges associated with chemical tagging, including a first constraint on the disrupted cluster mass function in the Milky Way, and how Gaia, as well as extragalactic IFU studies, could be informative in the studies of chemical tagging. I will also describe a new set of tools for efficient measuring multi-elemental abundances from large quantities of low-resolution LAMOST spectra, for constraining the binary fraction in the Milky Way, and for inferring asteroseismic parameters from spectra.

28

2017-09-20 Wed14:20~15:20R1203

Li-Ting Hsu[ASIAA]

WIRCam/CFHT Near-Infrared Survey and Photometric Redshifts in the Extended GOODS-North field

Abstract

To understand the evolution of galaxies, near-infrared (NIR) imaging is essential because: (1) NIR can used to identify Balmer break of galaxies at 1 < z < 4, (2) NIR luminosity reflects the stellar mass of galaxies, and (3) NIR is less affected by the dust extinction comparing to optical observation. In this work, we will present deep NIR images (J, H, and Ks) of the extended Great Observatories Origins Deep Survey-North (GOODS-N) field observed from the WIRCam/CFHT. The data reaches 5-sigma limiting AB magnitudes (in 2” aperture) of J=24.6 mag, H=23.8 mag, and Ks=24.1 mag over ~0.25 deg2. In the GOODS-N field, several deep multi-wavelength surveys have been carried out for various science goals, including radio survey from the VLA, FIR survey from the Herschel, MIR survey from the Spitzer, optical survey from the Subaru telescope, and X-ray survey from the Chandra space telescope. Our NIR survey can be an essential complementation in this field. In addition to the NIR images, we will also present photometric redshift (photo-z) results for non-X-ray and X-ray sources. For non-X-ray sources, we obtain the photo-z accuracy of sigma_NMAD=0.035 with the outlier fraction=7.2%. For X-ray sources, the photo-z accuracy of sigma_NMAD is 0.039 and the outlier fraction is 10.7%. Our photo-z quality is comparable to previous works in this field and show even smaller bias with respect to the spectroscopic redshift in general.

29

2017-09-13 Wed14:20~15:20R1203

Hung-Hsu Chan[NTU]

How do stars affect wave-dark matter?

Abstract

Wave dark matter (ψDM) consisting of a non-relativistic Bose-Einstein condensate, is considered to be a viable dark matter candidate. Due to the uncertainty principle that counters gravity below a Jeans scale, the small-scale structures are suppressed and a solitonic core persists in galaxy formation and evolution. We, for the first time, conduct ψDM simulations including stars. Nontrivial interactions between ψDM and stars are to be presented. ψDM lenses also show different strong lensing features from CDM lenses. The granularity in ψDM halos engenders anomalous fluxes of lensed images.

30

2017-09-06 Wed14:20~15:20R1203

George Djorgovski[Caltech]

Big Data Meet Big Black Holes: Quasars in the Time Domain

Abstract

Variability is one of the key observational properties of quasars, and it can be used as a probe of their fueling, physics, and evolution. A new generation of synoptic sky surveys, in combination with the novel data analytics tools, offers unprecedented data sets for the studies of quasars in the time domain. I will illustrate this with examples from the Catalina Real-Time Transient Survey (CRTS), which has an open and growing archive of 500 million light curves, including 350,000 spectroscopically confirmed quasars, with the time baselines ranging from 10 minutes to 10 years. This includes: a new approach to quasar discovery using a combination of variability and mid-IR colors from WISE, that will result in a catalog of at least a million new quasar candidates; the discovery of a characteristic time scale for a stochastic variability of quasars, that may probe the physics of their accretion disks; discoveries of type-changing quasars that show strong spectroscopic changes on the time scales of years, coupled with an anomalous variability; discovery of megaflares lasting a few years; and so on. Perhaps the most interesting is the discovery of periodically variable quasars, which we interpret as a signature of close (milliparsec scale) supermassive black hole (SMBH) binaries en route to a merger. Existence of such systems is expected from our understanding of hierarchical galaxy and SMBH assembly, and studies of this population can provide new insights into the final stages of SMBH mergers. Long wavelength gravitational waves from them may be detectable with the pulsar timing arrays in the next decade.

The abundances of heavy elements in planetary nebulae reveal the evolutionary past of the central star, and the future of the interstellar medium, but suffer from a major systematic uncertainty: abundances derived from emission lines formed by recombination exceed those from collisionally excited lines by a factor ranging from ~2 to nearly three orders of magnitude in the most extreme case. The discrepancy has been known since the 1940s but only now are its causes being tracked down. There is now substantial evidence for the presence of cold hydrogen-deficient material within the normal hydrogen-rich gas of planetary nebulae, which gives rise to strongly enhanced recombination line emission.
It has recently become clear that the most extreme abundance discrepancies occur in nebulae which have a close binary central star. I will discuss my recent work which has doubled the sample of nebulae with a close binary central star and known chemistry, placing new constraints on the origin of hydrogen deficient material and the cause of the abundance discrepancy.

32

2017-08-23 Wed14:20~15:20R1203

Mike Barlow[UCL]

Observations of Supernova Dust and Molecules

Abstract

Although a number of models for the formation of dust in the ejecta of
core-collapse supernovae (CCSNe) had predicted that between 0.1 and 1.0
Msun of dust could be formed per event, it was not until the 2009-2013
Herschel mission that direct observational evidence was obtained for the
presence of such large masses of dust in several young supernova remnants,
including Cas A, the Crab Nebula and SN 1987A. High angular resolution
submillimetre observations of SN 1987A with ALMA subsequently confirmed
that its cold dust emission originated from the inner expanding ejecta.
The presence of dust in CCSN ejecta can also be diagnosed and quantified from red-blue asymmetries in their late-time optical emission line profiles. I will summarise current results for SN dust masses based on these methods.
The ALMA observations of the ejecta of SN 1987A also revealed strong CO and SiO rotational line emission. Broad CO line emission has also been detected from the reverse shock region of Cas A, while ArH+ (argonium) rotational lines were first detected by Herschel from the Crab Nebula. These molecular lines have opened up the possibility of measuring supernova isotope ratios for the first time.

33

2017-08-16 Wed14:20~15:20R1203

Ing-Guey Jiang[NTHU]

Is there any Earth-like exoplanet at 1 AU from a G-type Star ?

Abstract

It has been a great success that with continuous effort of ground-based and space projects, thousands of exoplanets were found. In addition to introducing recent results and progress of my group's on-going planetary projects, the existence of Earth-like exoplanets at 1 AU from a G-type star will be addressed through planetary mass-period functions. The implications of this existence will be discussed.

34

2017-08-09 Wed14:20~15:20R1203

Tetsuya Hashimoto[NTHU]

Surface density: a new parameter in the fundamental metallicity relation of star-forming galaxies

Abstract

Star-forming galaxies display a close relation among stellar mass, metallicity and star-formation rate. This is known as the fundamental metallicity relation (FMR), and it has a profound implication on models of galaxy evolution. However, there still remains a significant residual scatter around the FMR. We show here that a fourth parameter, the surface density of stellar mass, reduces the dispersion around the FMR. In a principal component analysis of 29 physical parameters of 41,338 star-forming galaxies, the surface density is found to be the fourth most important parameter. The new four-dimensional fundamental relation forms a tighter hypersurface that reduces the metallicity dispersion to 50% of that of the FMR. We suggest that future analyses and models of galaxy evolution should consider the FMR in a four-dimensional space that includes surface density. The dilution time scale of gas inflow and the star-formation efficiency can explain the observational dependence on surface density.

35

2017-08-07 Mon14:20~15:20R1203

Hua-bai Li[CUHK]

*Special Seminar*Probing Star Formation from Hong Kong

Abstract

I moved to CUHK in Aug. 2013, right after the Protostars &
Planets VI conference, where we contributed a review chapter about the role of magnetic fields
(B-fields) in star formation [1]. The chapter concluded that B-field orientation should be quite
ordered from the cloud to core scales. We are trying to understand the consequence of such
kind of B-fields on cloud fragmentation [2], star formation rates [3] and turbulence
behaviors (anisotropy [4] and ambipolar diffusion), based on both observations and numerical
simulations. We are also building the polarimeter, a field mapping instrument, for ASTE. I look
forward to collaboration on these topics, especially from my hometown Taiwan.

The cosmic microwave background (CMB) continues to reveal new aspects of the large scale universe. For example, current projects are searching for evidence of primordial gravitational waves, for signatures sensitive to the sum of the neutrino masses, and for further understanding of the formation and growth of large structures under the influence of gravity in the accelerating universe. Technologies for ground-based and balloon-borne instruments measuring the polarization of the CMB have been well established and advanced in the last decade.
Two upgraded bolometric polarimeters on the Atacama Cosmology Telescope (ACT), the ACT Polarimeter (ACTPol) and the Advanced ACTPol, have made and will make sensitive measurements of the temperature and polarization in the Cosmic Microwave Background (CMB) with arcminute resolution. In this talk, I will focus on the instrumentation of these state-of-the-art arrays, especially the Advanced ACTPol ones. I will conclude with the results coming from the two-season cosmological results presented in Louis et al. (2016) and describe the current progress on the all three ACTPol seasons.

37

2017-08-02 Wed14:20~15:20R1203

Wing Ip[NCU]

News from Rosetta

Abstract

After a long journey, almost as long as the planning period, the Rosetta spacecraft finally reached the target comet, 67P/Churyumov-Gerasimenko, in August 2014. For nearly two years, Rosetta provided close-up looks of a cometary nucleus that came from the time of the solar system formation and a far-away place. In this talk, we will give a summary of some of the major results obtained by different instruments onboard the spacecraft and the Philae Lander. The research results produced by the NCU group will be described in passing.

Supersoft AGNs are a new class of AGNs which lack significant hard X-ray emission above ~2 keV. They may host intermediate mass black holes (IMBH) accreting in a poorly explored regime of parameter space, such as super Eddingtong accretion and extreme coronal condition. Their X-ray spectra are dominated by a soft thermal component, a form similar to
disk blackbody emission in stellar-mass BHs in their high/soft state. Though only three supersoft AGNs are reported to date, they show distinct X-ray variability behavior, some of them could be associated with TDE. In this talk, I will present the multi-wavelength characteristics of RX J1301.9+2746, the most distinct source of this kind. In particular, I will show our follow-up JVLA observations which reveal fast intraday radio variability, confining its origin likely from a compact jet. Such the unexpected presence of jets in a supersoft AGN challenges canonical theories of jet formation. All the results suggest that this AGN is an ideal laboratory for studying the universality of accretion/ejection coupling in BH accreting systems.

39

2017-07-19 Wed14:20~15:20R1203

Wladimir Lyra[CSUN]

Evolution of Circumstellar Disks and Planet Formation

Abstract

During the first million years of evolution, nascent planetary systems are embedded in dense disk-shaped clouds of gas. These "circumstellar disks" are home to a myriad of hydrodynamical processes, which bring about turbulence and the emergence of viscous-like behavior, enabling accretion of gas onto the forming star. Meanwhile, micron-sized dust grains embedded in the disk are growing into pebbles and rocks. Turbulence has a positive effect on these small solids, concentrating them into transient high pressure regions for long enough to achieve gravitational collapse through pebble accretion into km-sized bodies, forming the first planetesimals. Giant storm systems in the disk, similar to Jupiter's Great Red Spot, may exist in quiescent zones of the disk. These are even more prone to collecting solid material, producing the first terrestrial planets and cores of giant planets. In this talk I will discuss the state of the art and recent advances in the field of planet formation, as well as pressing problems such as the structure observed in high resolution images of circumstellar disks, and how to interpret them.

40

2017-07-12 Wed14:20~15:20R1203

Renyu Hu[JPL]

Studying Planetary Atmospheres in an Exoplanet Era

Abstract

The number of planets we know increased by two orders of magnitude in the past decade. Many of the planets discovered outside the solar system, i.e., the exoplanets, have surprising traits, including having orbital periods of a mere few days, being larger than Earth and smaller than Neptune, and having atmospheric compositions where data suggest deviation from chemical equilibrium. These discoveries necessarily reorient our study of planetary atmospheres. I will discuss how observations of exoplanet atmospheres help us better understand the physical and chemical processes that control planetary atmospheres as well as the evolution of planets. For example, strong stellar irradiation and intermediate size of some exoplanets enable the formation of helium atmospheres, resulting in distinctive remote sensing spectral features. Transit observations of Hubble and JWST thus provide the opportunity to study the atmospheric evolution of super-Earths and sub-Neptunes. Looking ahead, I will conclude by describing pathways forward to directly image and characterize cold planets at wide orbital separations and search for potential signs of life from alien worlds.

41

2017-06-30 Fri14:20~15:20R1203

Charling Tao[Tsinghua University]

*Special Seminar*What do we know about the Dark Universe?

Abstract

In this talk I will review our present knowledge about the Dark Universe and the main research areas which are currently shedding some light. Cosmology has become a science. We measure with precision the extent of our ignorance. The Universe today is dominated by dark energy and dark matter.
Dark Energy could well reduce to the cosmological constant, and within 10 years, we should have results from many surveys which either will find a deviation from a cosmological constant or we will have to explain why the dark energy is so close to a cosmological constant and is not. Unless there is a modification of gravity, our Galaxies and the universe has Dark Matter which nature is still unknown. I will describe some of the attempts to unveil its nature, and maybe open up in the future a new field of Dark Matter astronomy, as we are witnessing today the beginning of gravitational waves astronomy.

42

2017-06-29 Thu14:20~15:20R1203

Chia-Hsun Chuang[AIP Potsdam]

*Special Seminar*The Map of the Universe Based on the Positions of Quasars

Abstract

During the first two years of the SDSS’s Extended Baryon Oscillation Spectroscopic Survey (eBOSS), astronomers measured accurate three-dimensional positions for more than 147,000 quasars. We have created the first map of the large-scale structure of the Universe based entirely on the positions of quasars. But to use the map to understand the expansion history of the Universe, we had to go a step further, using a technique involving studying “baryon acoustic oscillations” (BAOs). BAOs are the present-day imprint of sound waves which travelled through the early Universe, when it was much hotter and denser than the Universe we see today. People have previously used the BAO technique on nearby galaxies and then on intergalactic gas distributions to push this analysis farther and farther back in time. The current results cover a range of redshift where they have never been observed before (z ~ 1.5).
The results of the new study confirm the standard model of cosmology that researchers have built over the last twenty years. In this standard model, the Universe follows the predictions of Einstein’s General Theory of Relativity -- but includes components whose effects we can measure, but whose causes we do not understand. Along with the ordinary matter that makes up stars and galaxies, the Universe includes dark matter - invisible yet still affected by gravity - and a mysterious component called “Dark Energy”. Dark Energy is the dominant component at the present time, and it has special properties that cause the expansion of the Universe to speed up.

43

2017-06-28 Wed14:20~15:20R1203

Juan-Carlos Algaba[KASI]

Interferometric Monitoring of Gamma-Ray Bright AGNs: Exploring the Variability of the Flat Spectrum Radio Source 4C38.41

Abstract

The Interferometric Monitoring of Gamma-ray Bright AGNs (iMOGABA) is a monitoring program for about 30 gamma-ray bright AGNs using the Korean VLBI Network (KVN) at simultaneous frequency bands (22, 43, 86 and 129 GHz) aimed at studying the origins of the gamma-ray flares of AGNs. Here We present observations of the flat spectrum radio quasar 4C 38.41 as part of the iMOGABA program combined with additional observations in radio, optical, X-rays and gamma-rays carried out between the period 2012 March - 2015 August. The monitoring of this source reveals a significant increase in its activity in the radio bands, which correlates with other bands from sub-millimeter to gamma-rays. The epochs of the maxima for the two largest gamma ray flares seem to coincide with the ejection of two respective new VLBI components. The evolution of the flares probes the adiabatic losses in agreement with the shock-in-jet model. Derived synchrotron self absorption magnetic fields, of the order of 0.1 mG, do not seem to dramatically change during the flares, and are much smaller than the estimated equipartition magnetic fields, indicating that the source of the flare may be associated with a particle dominated emitting region. This is consistent with considerations suggesting that this region may be located near but downstream the acceleration and collimation region.

44

2017-06-21 Wed14:20~15:20R1203

Yu-Yen Chang[ASIAA]

Host Galaxies of Obscured AGNs and their Environment

Abstract

I will present our recent results on mid-infrared selected active galactic nuclei (AGNs). We derived their stellar masses, star formation rates, dust properties, AGN contributions, as well as obscurations by fitting their optical to far-infrared photometry through the state-of-art spectral energy distribution (SED) technique. Our obscured AGNs by infrared selection are not significant different from the star-forming sequence. We confirm our previous finding about compact host galaxies of obscured AGNs at z~1, and find that galaxies with 20-50% AGN contributions tend to have smaller sizes, by~25-50%. Besides, we show that high merger fraction up to 0.5 happens to the most luminous (LIR ~46 ergs/s) AGN host and non-AGN galaxies, but not to the whole obscured AGN sample. Moreover, merger fraction has dependence on the total and star-forming infrared luminosity, rather than the decomposed AGN infrared luminosity. Our results suggest that major merger is not the main driver of AGN activities, and obscured AGNs might be triggered by internal mechanisms, such as secular process, disk instabilities, and compaction in a particular evolutionary stage. I will also discuss the role of environment on these obscured AGNs, based on new data from JCMT Large Programs.

45

2017-06-19 Mon14:20~15:20R1203

Yapeng Zhang[CUHK]

*Special Seminar*Magnetic field orientations and star formation rates

Abstract

The relation between star formation rates (SFRs) and magnetic field
is still a mystery. Through a comparison between the surveys of SFRs
and a study of cloud–field alignment—which revealed a bimodal (parallel
or perpendicular) alignment—we show that the perpendicular alignment
tends to have lower SFRs per solar mass. This indicates that B-fields are
a primary regulator of SFRs: a perpendicular cloud-field alignment has
higher magnetic flux than parallel cases and the support of the gas
against self- gravity is stronger. Moreover, cloud fragmentation and magnetic field alignment is found to be selfsimilar (e.g. Li et al. 2015). Whether the bimodal SFR is also
selfsimilar can only be answered with a higher resolution of magnetic-
field detection. I will also introduce APol, the ASTE Polarimeter, which I
am leading to build for this purpose.

The dwarf spheroidal galaxies (dSphs) in the Milky Way are excellent laboratories to shed light on fundamental properties of dark matter because these galaxies are the most dark matter dominated systems. DSph galaxies also have the advantage that we can measure very accurate line-of-sight velocities for resolved member stars. Therefore, using these high-quality data, we are able to constrain internal structure of their dark halos. In the first part of my talk, I will present the constraint on candidate dark matter particles through indirect searches for their annihilations from non-spherical dark halo in the Galactic dSphs. I also show that Prime Focus Spectrograph mounted on Subaru telescope will play an important role in getting an insight into the nature of dark matter particles by synergy between space and ground-based telescopes. In the second part, I will propose the universal dark halo scaling relation for the dSphs. This scaling relation would not be largely affected by any baryonic feedbacks, hence it is good tracer to compare between observed and simulated dark halos. Using high-resolution N-body simulations based on Lambda cold dark matter (LCDM) universe, we find that this relation from observed dSphs is in good agreement with those from pure dark matter simulations. Therefore, LCDM models can reproduce the observed dark halo properties even on small mass scales without baryonic uncertainties.

47

2017-06-14 Wed14:20~15:20R1203

Naonori Sugiyama[Kavli IPMU]

Kinematic Sunyaev-Zel'dovich Effect

Abstract

Over the past few years, cosmologists have been able to make the first detections of the kinematic Snuyaev-Zel'dovich (kSZ) effect by combining galaxy data with measurements from CMB experiments. The kSZ effect is well-suited for studying properties of the optical depth of halos hosting galaxies or galaxy clusters. As the measured optical depth via the kSZ effect is insensitive to gas temperature and redshift, the kSZ effect can be used to detect ionized gas that is difficult to observe through its emission, so-called "missing baryons". This work presents the first measurement of the kSZ signal in Fourier space. While the current analysis results in the kSZ signals with only evidence for a detection, the combination of future CMB and spectroscopic galaxy surveys should enable precision measurements. This talk emphasizes the potential scientific return from these future measurements.

We use the Subaru Hyper Suprime-Cam (HSC) to conduct a high-cadence (2 min sampling) 7~hour long observation of the Andromeda galaxy (M31) to search for the microlensing magnification of stars in M31 due to intervening primordial black holes (PBHs) in the halo regions of the Milky Way (MW) and M31. The combination of an aperture of 8.2m, a field-of-view of 1.5 degree diameter, and excellent image quality (~ 0.6'') yields an ideal dataset for the microlensing search. If PBHs in the mass range M_PBH=[10^{-13},10^{-6}]Msun make up a dominant contribution to dark matter (DM), the microlensing optical depth for a single star in M31 is tau~10^{4}-10^{-7}, owing to the enormous volume and large mass content between M31 and the Earth. The HSC observation allows us to monitor more than tens of millions of stars in M31 and in this scenario we should find many microlensing events. To test this hypothesis, we extensively use an image subtraction method to efficiently identify candidate variable objects, and then monitor the light curve of each candidate with the high cadence data. Although we successfully identify a number of real variable stars such as eclipse/contact binaries and stellar flares, we find only one possible candidate of PBH microlensing whose genuine nature is yet to be confirmed. We then use this result to derive the most stringent upper bounds on the abundance of PBHs in the mass range. When combined with other observational constraints, our constraint rules out almost all the mass scales for the PBH DM scenario where all PBHs share a single mass scale.

The standard galaxy formation scenario in the popular LCDM cosmogony has been very successful in explaining the large-scale distribution of galaxies. However, one of the failures of the theory is that it predicts too many satellite galaxies associated with massive galaxies compared to observations, which is called the missing satellite galaxy problem. Isolated groups of galaxies hosted by massive early-type galaxies are ideal laboratories for finding the missing physics in the current theory.
We discover through a deep spectroscopic survey of galactic satellite systems that bright isolated early-type galaxies have almost no satellite galaxies fainter than the r-band absolute magnitude of about -14. The cutoff in the satellite galaxy luminosity function is at somewhat brighter magnitude of about -15 for early-type satellites. Physical properties of the observed satellites depend sensitively on the host-centric distance. All these are strong evidence that galactic satellites can be significantly affected due to astrophysics of satellite-host galaxy interaction. Previously, the faint end of the luminosity function of satellite galaxies has been measured only for late-type host systems or down to absolute magnitudes brighter the cutoff. Our work expands our knowledge to early-type host systems and down to absolute magnitude much fainter than -14.
A recent state-of-the-art hydrodynamic simulation of galaxy formation does not reproduce such a cutoff in the satellite galaxy luminosity function. But the past history of the simulated satellites demonstrates that many satellite galaxies evolve to become fainter than the cutoff magnitude by the present epoch through fatal encounters with the host or other satellite galaxies. This leaves the hope that the missing satellite galaxy problem could be mitigated if the astrophysics of galaxy interaction is more elaborated in the theory.

50

2017-06-06 Tue14:20~15:20R104, CCMS

Changbom Park[Korea Institute for Advanced Study (KIAS)]

*ASIAA/NTU Joint Colloquium*Cosmology with the Large-scale Structures of the Universe

Abstract

In the first part of my talk I will briefly review sciences with the large-scale structures of the universe. In particular, I will introduce how the growing galaxy redshift data can be used to constrain cosmological models and galaxy formation theories.
In the second part a new method for measuring the cosmological parameters governing the expansion history of the universe will be introduced. The method uses the Alcock-Paczynski (AP) test applied to the overall shape of the galaxy two-point correlation function along and across the line-of-sight. We applied this method to simulated data and also to a recent galaxy survey data to obtain an impressive constraint on the dark energy equation of state and matter density parameter Ωm.

51

2017-06-05 Mon14:20~15:20R1203

Chin-Ping Hu[The University of Hong Kong]

*Special Seminar*Magnetic Field Effects on Pulsars

Abstract

Pulsars are fast-rotating neutron stars with strong magnetic fields. Magnetars are an extreme group of pulsars with extraordinarily strong magnetic fields of $10^{14}$--$10^{15}$ G, and remarkable for the bursting activities and high X-ray luminosities powered by their high magnetic field. However, recent discoveries blurred the boundary between magnetars and rotation-powered pulsars (RPPs). In this talk, I will introduce the recent works on the high-magnetic-field RPPs, especially the youngest ones of J1846-0258, J1119-6127, and B1509-58. Young and high-magnetic-field RPPs have surface temperatures between the magnetars and canonical RPPs, indicating that high-magnetic-field RPPs are potential bursters and may contain toroidal magnetic fields according to the magneto-thermal evolution model. This model implies that the toroidal field could play an important role in bursting rate and the temperature anisotropic. Our recent work on the statistics of magnetars' pulse profiles agreed on this implication well. Finally, I will introduce the possible connection between the magnetars and the accreting pulsars in ultraluminous X-ray sources. Toroidal or multi-polar magnetic fields are necessary to interpret the high luminosities and the observed spin-up rates, indicating that ultraluminous pulsars are possibly powered by magnetars.

52

2017-06-02 Fri15:20~16:20R1203

Ming Sun[University of Alabama Huntsville]

Study Baryon Physics with Galaxy Groups and Clusters

Abstract

Galaxy groups and clusters are the least massive systems where the bulk of baryons are accounted for and also the most massive systems that are gravitationally bound. Baryons locked into stars and baryons remaining diffuse provide orthogonal constraints on cosmic structure formation, which makes groups and clusters ideal systems to study baryon physics. In this talk, I will summarize our results on X-ray scaling relations of local galaxy groups and clusters. By stacking the Chandra data of 320 galaxy clusters, we are able to track the X-ray emission beyond the virial radius and unambiguously detect the steepening of the density profile with radius (beta ~ 1 at r_200 and beyond). The universal baryon fraction is also recovered at r_200. The stacked emission is also significantly different along the major and minor axes of the hot gas distribution, implying the detection of cosmic filaments. We further applied the weak self-similarity of the emission measure profiles at large radii to obtain good constrains of cosmological parameters, which provides an independent, direct method solely based on observed quantities. The stacking work has also been extended to lower-mass halos like galaxy groups and I will highlight our recent results on a local galaxy group with over 400 ks Chandra data. In the end, I will discuss our results on a sample of the most massive MaxBCG clusters, which sheds light on the puzzling offset between the Planck stacked SZ signals and the predicted values from the X-ray pressure template.

53

2017-05-24 Wed14:20~15:20R1203

Takahiro Nishimichi[IPMU]

Analytical and numerical approaches to cosmic large scale structures

Abstract

Theoretical tools for accurate predictions of cosmological structure formation are significantly updated in this decade in light of recent and future observational programs. They include efficient calculations of perturbative expansion based on re-organization of the diagrams and emulators constructed based on a series of numerical simulations. I will present our recent studies on this topic with particular attention to their limitations and future prospects.

54

2017-05-18 Thu14:30~15:30R1203

Eleonora Ammannito[Italian Space Agency]

*Special Seminar*Mineralogical mapping across the main belt, Vesta and Ceres as test cases

Abstract

From July 2011 to August 2012, Dawn spacecraft orbited around Vesta. It escaped then for Vestan gravitational well and since January 2015 is acquiring data at Ceres. The Visible InfraRed mapping Spectrometer (VIR) mapped Vestan and Cerean surfaces acquiring VIS/NIR spectra (0.5 µm -5.0µm) with resolutions ranging from 70m to 800m. Vesta and Ceres have a completely different composition. Vestan surface is dominated by basalt and is genetically linked to HED meteorites. Ceres on the other hand has on the surface mainly aqueous alteration products like clays and does not have a clear match in the meteorite collection. These two different surfaces are indicative of a different evolutionary path of the two most massive objects of the main belt.

55

2017-05-17 Wed11:00~12:00R1107

Karl Ziemelis[Nature]

*Special Seminar*Inside Nature

Abstract

Since its launch in 1869, Nature has seen its mission as two-fold: facilitating the prompt communication of the most important scientific developments to the relevant research communities, while at the same time fostering a greater appreciation of these great works of science amongst the wider public. Although the publishing landscape for scientific research is currently undergoing a period of unprecedented change, these core principles remain largely unchanged. In this talk, I will endeavour to shed light on how Nature editors apply these principles in practice, and so determine which few of the many excellent research submissions that we receive make it through to publication.

I will first briefly review the molecular gas content of early-type
galaxies. I will show not only that they unexpectedly harbour much
cold gas, but also that it is the best tracer of the circular
velocity, thus allowing accurate spatially-resolved dynamical mass
measurements in galaxies across the Hubble sequence. Second, I will
explore the use of molecular gas for studies of the Tully-Fisher
(luminosity-rotational velocity) relation of galaxies to high
redshifts. I will highlight the work done to establish local (z=0)
benchmarks and will discuss the challenges posed by systematic effects
when comparing nearby and distant galaxies. Third, I will demonstrate
that CO can be used to easily and accurately measure the mass of the
supermassive black holes lurking at galaxy centres. I will discuss
substantial ongoing efforts to do this and present many spectacular
new ALMA measurements, that open the way to literaly hundreds of
measurements across the Hubble sequence with a unique method. I will
also hint at how the same data allow to study the spatially-resolved
properties of giant molecular cloud populations in non-local galaxies
for the first time, providing a new tool to understand and contrast
the star formation efficiency of galaxies on cloud scale.

57

2017-05-10 Wed14:20~15:20R1203

Kevin Koay[ASIAA]

Interstellar scintillation as micro-arcsecond scale probes of compact radio AGNs

Abstract

The variability of compact AGNs on timescales of hours and days observed at cm-wavelengths is predominantly caused by scattering in the ionized interstellar medium (ISM) of our Galaxy. With the ISM as an AU-scale interferometer, interstellar scintillation (ISS) provides an exquisite probe of the micro-arcsecond scale structure of AGNs. I present results from the Micro-arcsecond Scintillation-Induced Variability (MASIV) Survey of ~500 compact AGNs and its follow-up observations. I will discuss the dependence of ISS on intrinsic AGN properties, including their gamma-ray loudness, radio spectral indices, optical spectral classification, redshift, and intrinsic variability. I will show how we can use ISS to probe the source size-redshift relation of compact AGNs, and place strong constraints on the turbulent properties of the intervening intergalactic medium. Future surveys of ISS with highly-sensitive radio telescopes such as the SKA will potentially probe the micro-arcsecond structure of faint (~100 muJy to 10 mJy) AGNs, thereby complementing studies at comparable angular resolutions with Space-VLBI and mm-VLBI which at present are limited only to the brightest AGNs.

58

2017-05-03 Wed14:20~15:20R1203

Xiaohu Li[ASIAA]

Progress, Challenges, and Opportunities in the Study of “Molecular Factories” in Space

Abstract

On the Asymptotic Giant Branch (AGB), stars that have reached the end of their lives eject gas and dust to their surroundings, forming a circumstellar envelope (CSE) containing a rich variety of complex molecules. These CSEs are true “molecular factories” in space, attracting great interests from both astronomers and chemists. Thanks to the progress from high-quality observations (e.g., Herschel, ALMA, etc.) and the improvement in the accurate reaction rates of the most abundant molecules, plus the development of new astrochemical models, much of successes have been made in the understanding of the compositions and chemistry of these “molecular factories”. In this talk, I will briefly introduce our previous and recent work during the investigation of the CSEs of all types of AGB stars. I will also talk about major challenges and opportunities we have in the next few years.

59

2017-04-26 Wed14:20~15:20R1203

Ai-Lei Sun[ASIAA]

The many facets of AGN feedback -- a multi-wavelength view of galactic outflows

Abstract

Active galactic nuclei (AGN) feedback is now a standard ingredient in galaxy evolution models. Popular models suggest that during the quasar phase, gas is driven out of the galaxy in the form of outflows, shutting off star-formation and black hole growth, leading to the observed quiescent galaxy population and the black hole -- galaxy correlations, but many assumptions require observational supports. Observations have discovered galactic outflow in the luminous quasar, but their structure is surprisingly complex, involving a wide range of gas phases from cold molecules to hot X-ray emitting gas. Multi-wavelength coverage is needed for a comprehensive picture. I summarize recent optical, radio, and X-ray observations of AGN outflows in nearby luminous quasars, and what do we learn about their occurrence rate, composition, and energetics, as well as the life cycles of AGN feedback. I end with discussing how on-going and future optical surveys could help us study this rare and intriguing phenomenon of AGN feedback.

60

2017-04-24 Mon14:20~15:20R1203

Jesus Toala[ASIAA]

*Special Seminar*X-ray Emission as a probe of Stellar Evolution

Abstract

Very massive stars are the main actors in shaping and chemically enriching the ISM in the
galaxies we see. They do so by a combination of their stellar winds, proper motions, strong
ionising photon fluxes, and supernova explosions. These produce cavities in the ISM that can
be studied with X-ray observatories. In this talk I review our current understanding of the
production of diffuse X-ray emission towards the nebulae carved by massive stellar feedback.

61

2017-04-21 Fri14:20~15:20R1203

Laurent Pagani[Observatoire de Paris]

*Special Seminar*Deuterium, a swiss-knife to study star-formation

Abstract

Though we understand the main steps which lead from diffuse gas to a newborn star with its nascent planets, a number of details remain obscur and need clarification. One of the least understood steps is the formation and collapse of the prestellar core, in the dark cloud. This is due to the core being extremely cold (down to 6 K), deeply embedded in the cloud and largely depleted of most molecular species. Therefore almost no tracer is available to study this phase in detail. Apart from dust itself (it would require a second talk to discuss it), the main tracers are H2D+, N2H+, N2D+ and DCO+ (the NH3 family is another possibility). 3 species out of 4 carry a Deuterium. Why are they abundant enough to be detected when the cosmic D/H ratio is as low as 10^-5 and what can we learn from their presence ? In the presentation, I will illustrate 3 different measurements we can perform thanks to the peculiar deuterium chemistry: the age of clouds, the age of prestellar cores and the depletion profile of CO and N2 in these cores, which is a prerequisite to study the interaction of grain surface chemistry (ices) with the gas phase in the dense cores. Deuterium appears as a swiss-knife to study star formation.

62

2017-04-19 Wed14:20~15:20R1203

Andrew Youdin[University of Arizona]

The Route to Planetesimals

Abstract

It has long been difficult to understand how dust grains could grow past the “meter-size barrier” to become super-km scale planetesimals, the solid building blocks of planets. Daunting obstacles include the rapid radial drift of solids towards the star and the tendency of many collisions to result in destruction or bouncing instead of growth. The route to planetesimals focuses on two broad mechanisms. First finding the circumstances that may lead to more effective collisional growth towards or even beyond the meter-size barrier. Second, (aero)dynamical mechanisms to concentrate smaller solids into gravitationally bound planetesimals. The classic dynamical mechanism is a gravitational instability of the particle disk. In the streaming instability mechanism, drag forces and radial drift can automatically produce strong particle clumps. Recent simulations have explored the viability of the streaming instability across a broad range of parameter space. I will asses the viability of the streaming instability and other planetesimal formation mechanisms, including a discussion of the large scale dust structures observed in protoplanetary disks.

63

2017-04-12 Wed14:20~15:20R1203

Hayato Shimabukuro[Observatoire de Paris]

21cm cosmology meets artificial neural networks

Abstract

The 21 cm signal from the Epoch of Reionization should be observed within the next decade. To extract from the observed data constraints on the parameters describing the underlying astrophysical processes, inversion methods must be developed. Here we test possible inversion method for EoR parameter reconstruction: artificial neural networks (ANN). We find that the quality of the parameter reconstruction depends on the sensitivity of the power spectrum to the different parameters at a given redshift, that including thermal noise and sample variance decreases the quality of the reconstruction and that using the power spectrum at several redshifts as an input to the ANN improves the quality of the reconstruction.

Young galaxies with strong star formation activity are likely sources of
cosmic ray particles. At high-energies, these particles interact with
the baryon and radiation fields of the galactic environment via
hadronuclear, photo-pair and photo-pion processes to produce charged and
neutral pions, neutrons and protons. At lower energies, they can
interact by collisional ionization. In both cases, the effect is to
drive a heating process in the interstellar medium and beyond. The
distribution of this heating effect is governed by the galactic magnetic
field in the case of low-energy cosmic rays which effectively become
‘locked’ and diffuse predominantly along field lines. At high-energies,
the cosmic ray heating is governed more strongly by the multi-phase
interstellar density field, with the particles being more freely able to
diffuse throughout the magnetic field. This talk addresses the
interactions between these low and high-energy particles and the
partially ionised gases and dense molecular clouds in starbursting
protogalactic environments. We calculate the energy deposited by cosmic
rays as they propagate in and around their host galaxy and demonstrate
how this affects the thermal conditions and star formation in the host
galaxy and its neighbours.

65

2017-03-30 Thu14:20~15:20R1203

Werner Krauth[Ecole Normale Supérieure]

*Special Seminar*Research and higher education in France, between Organizations, Schools and Universities

Abstract

A mirror of the multi-faceted research environment in most countries in the world, and in particular in Europe, the French academic environment is organized by a considerable number of actors, in a way that is not totally transparent from the outside. Nevertheless, the system produces a very stable environment, and provides opportunities for research and study at the highest level of excellence. In this presentation, I will (attempt to) provide an introduction to French research organization, with a focus on my discipline, physics, and on my own institution, Ecole normale supérieure, in Paris.

66

2017-03-29 Wed14:20~15:20R1203

Kenny Vilella[Institute of Earth Sciences, Academia Sinica]

What thermal convection can tell us about planetary observations: applications to Pluto and habitability of exoplanets

Abstract

Thermal evolution of planetary bodies is mainly controlled by its interior thermal convection and affect importantly its atmosphere and surface processes. The observations of its direct and indirect implications provides important constraints. For instance, the polygonal network found on the nitrogen glacier Sputnik Planitia (SP) on Pluto's surface (Stern et al. 2015), indicates that thermal convection operates within SP, which in turn suggests a large glacier thickness. Thermal convection, therefore, gives information that help the interpretation of planetary observations. For instance, the thickness of SP inferred by thermal convection indicates that a deep ocean is required to explain the location of SP on the equator. Thermal convection and planetary observations are therefore closely linked.

Here I present different approaches to study thermal convection and I emphasize the important link between our work and planetary observations. First, I investigate thermal convection within SP suggested by its surface polygonal network. Based on complex 3D-numerical simulations conducted for a large range of convective system, I conclude that only internal heating may produce such a surface pattern. However, there is no clearly identified source of internal heating within SP. I propose that the surface temperature variations caused by the variation in Pluto's orbit may be an appropriate source of heating. Second, I follow a parameterized approach to predict the occurrence of partial melting in exoplanets. Partial melting being necessary to maintain an atmosphere over a long period of time, which is a prerequisite for the presence of life. I found that moderate size planets are the most likely to be habitable, which show the importance of detecting Earth-size exoplanets.

Hydrodynamic interactions are ubiquitous. I have devoted myself in various topics related to hydrodynamic interactions encoded in the celestial patterns surrounding various astronomical objects including evolved stars, young stellar clusters, merging black hole pairs, etc. In this talk, I will show that these various phenomena have similarities and cross-connection in a theoretician's point of view and provide some potential applications and directions.

68

2017-03-23 Thu14:20~15:20R1203

Ke-Jung Chen[NAOJ]

*Special Seminar*Lighting up the Universe with Extreme Supernovae

Abstract

Recent all-sky transient searches have discovered new and unexpected explosion types
that fall outside traditional SN classification schemes. These exotic outliers in many cases
are due to the deaths of massive stars and therefore may have been prevalent in the
primordial universe because the Pop III IMF is thought to be top-heavy. Depending on the
mass of the progenitor, these outliers may be faint, magnetar-powered, pair-instability, or
general relativistic instability SNe, all of which have unique observational signatures.
Some of these events are superluminous, 10-100 times brighter than normal supernovae,
and may produce energetic UV, X-ray, or gamma-ray bursts. Their extreme luminosities
enable their detection at z > 10 and they are ideal probes of the primordial universe at
cosmic dawn, prior to the advent of the first galaxies. Here, we examine these exotic
explosions with state of the art 3D radiation-hydro simulations that bridge all spatial scales
from the central engine to breakout into the IGM, where observational signatures can be
computed. We discuss the coevolution of radiation and turbulent mixing in SN ejecta
and present realistic light curves for these explosions for JWST and the coming generation
of extremely large telescopes (ELTs). Detection rates for Pop III SNe can place useful constraints
on the primordial IMF, and their nucleosynthetic yields can be used to study the chemical
compositions of extreme metal poor stars.

69

2017-03-22 Wed14:20~15:20R1203

Ziri Younsi[University of Frankfurt]

Imaging Black Holes - Shadows, Accretion and Variability

Abstract

In the coming months and years mm-VLBI observations of supermassive black holes using the Event Horizon Telescope (EHT), most notably of Saggitarius A* and M87, are expected to verify the existence of astrophysical black holes through detection and measurement of the black hole shadow. Although the mathematical description of a black hole shadow is straightforward, its observational appearance is strongly governed by the (thermo)dynamics and geometrical structure of the surrounding accretion flow. This accretion flow, particularly on event horizon-scales, is turbulent and time variable, and must be modelled using general-relativistic magnetohydrodynamical (GRMHD) simulations. The propagation of radiation and therefore the appearance of shadow images, spectra and lightcurves are calculated using GR radiation transport (GRRT). Here we combine GRMHD and GRRT calculations to derive observational predictions of what upcoming VLBI observations of Sagittarius A* are expected to observe, addressing questions concerning variability therein and also discussing the possibility of testing the Kerr black hole hypothesis and constraining other black hole solutions and theories of gravity.

Planets are not born in their final state; rather, they change significantly over their lifetimes. Understanding how planets evolve has been a central question since the discovery of the first exoplanets. The first few hundred million years are thought to be the most formative, but planets in this age range are also the most difficult to identify and characterize. Instead, research has focused on inferring the history of planets through patterns in the population of older systems. In this talk I will discuss how this paradigm is shifting, as novel search techniques and new missions have enabled our discovery of Earth- to Jupuiter-size planets as young as 10 Myr. These discoveries have altered our understanding of how planets migrate and lose atmosphere, but raise further questions about the physical drivers of these changes. The upcoming TESS mission will discover hundreds more young planets, including analogues of a young Earth. Combined with follow-up from new NIR spectrographs (e.g., SPIRou on CFHT, IRD on Subaru), the TESS sample will enable new tests of planet formation and evolution through population statistics. Eventually, JWST, SPICA, and 30m-class telescopes can be used to study the atmospheres of young, rocky planets, providing unique insight into the history of potentially habitable planets.

One of the promising cosmological probes in the next decades is the CMB polarization. While CMB temperature anisotropies have been already measured very precisely, CMB polarization, in particular a twisting pattern in the polarization map (B mode) is not well measured. The detection of B mode at more than degree angular scale opens new window into the inflationary universe and high energy physics beyond the standard model. Precise polarization data also enables us to measure gravitational lensing of CMB which is a key probe to understand the properties of neutrinos, dark matter and dark energy. In this talk, I will present analysis of the gravitational lensing and cosmic birefringence measurements with CMB polarization data taken from BICEP2/Keck Array experiments. I will also talk about synergy between CMB experiments and galaxy surveys such as the galaxy-lensing cross correlation with Subaru-Hyper Suprime Cam and CMB experiments, and delensing B mode with mass tracers.

72

2017-03-15 Wed14:20~15:20R1203

Sofia Wallstrom[ASIAA]

The death throes of massive stars

Abstract

Massive evolved stars affect their local surroundings as they go through phases of intense mass-loss and eventually explode as supernovae, adding kinetic energy and freshly synthesised material to the interstellar medium. Over time, these processes affect the chemical evolution of the interstellar medium on a galactic scale. I will here present my PhD research, which probed the death throes of massive stars at various stages.
First, CO observations were used to study the circumstellar environment of a massive star, the yellow hypergiant IRAS 17163-3907. Observations with APEX and ALMA ACA reveal a complex environment with several distinct components: a fast recent stellar wind of 100 km/s, a clumpy CO ring which appears to be a torus ejected by the star several thousand years ago, and a unidirectional bright spur extending from the star to the clumpy ring. These asymmetries are not seen in infrared dust observations, and demonstrate the complexity of massive evolved stars and the need for high resolution molecular observations to understand them.
Next, observations of CO lines in the supernova remnant Cassiopeia A were used to study the effect of the reverse shock on supernova ejecta. A large column density of warm CO was found, which has most likely re-formed after the passage of the reverse shock. The high temperature and density implies that thermal conduction by electrons may be an important process for the evolution of dense ejecta knots, with implications for the survival of supernova dust.
Finally, the contribution of massive stars to galactic chemical enrichment was investigated indirectly with
measurements of isotopic ratios in a molecular absorber at z=0.68 towards B0218-211. The ratios at z=0.68 were found to be very different from those in the solar neighborhood, but similar to the ratios found in another absorber at z=0.89 and in starburst galaxies. The interpretation of these ratios is as a signature of enrichment mainly by massive stars.

It has recently become possible to perform large-scale cosmological simulations incorporating gas and enough physical processes to roughly reproduce the distribution of matter observed in the Universe. Our simulations have allowed us to resolve several long-standing problems in astrophysics, as well as suggesting new lines of investigation. I will describe in particular my work on the distribution of neutral hydrogen absorbers and galaxy clusters, both of which have implications for cosmology. I will then discuss my recent work on the implications of the LIGO gravitational wave detection for primordial black holes, which raises the exciting possibility that LIGO may have detected the dark matter.

74

2017-03-13 Mon14:20~15:20R1203

Baobab Liu[ESO]

*Special Seminar*Star formation: previous developments and future

Abstract

Limited by the coarse angular resolutions and/or the poor sensitivities of the previous generation (sub)millimeter telescopes (SMT, CSO, IRAM, SMA, Herschel, Planck), significant efforts and resources have been devoted to improving the constraints on a few "macro phenomenological correlations", such as the star-formation (e.g., Kennicutt-Schmidt law), Larson's laws, etc. While these laws are almost treated as fundamental physics laws, and have been routinely compared with any new observational measurements, the micro physics including how the stellar cluster-formation is related to an interplay between the supersonic gas motions and self-gravitational contractions, remain poorly understood. As an example, the meaning of the term "turbulence" has been rather ambiguous for the community of star-formation. In this talk, I will present our preliminary developments about how images of molecular cloud structures with extremely high spatial and intensity dynamic ranges may enable discriminating a variety of physical conditions, and how such developments can be prosecuted with the facilities of Taiwan and EAO.

75

2017-03-09 Thu14:20~15:20R1203

Geoff Bower[ASIAA]

*Special Seminar*Localization of the Fast Radio Burst 121102

Abstract

Fast radio bursts (FRBs) are millisecond-duration, highly-dispersed radio wavelength pulses. Based on their large dispersion measure, FRBs appear to originate from extragalactic distances implying extreme luminosities that are not seen in any galactic sources. Progress in understanding FRBs has been slow because the discovered events have had >arcminute localization, making association with galaxies or galactic objects impossible. Currently, there are more theories than FRBs, which number about 20. I will describe here the first arcsecond localization of an FRB. Using the Very Large Array (VLA) and other radio telescopes, we have shown that FRB 121102 is associated with a faint persistent radio source and a faint galaxy. Gemini observations provided the redshift (z~0.2) and identification of the galaxy as a dwarf with significant star formation and low metallicity. I will discuss the implications of this discovery for our understanding of FRBs and the possibility of using FRBs to study the intergalactic medium.

76

2017-03-08 Wed14:20~15:20R1203

Xuan Fang[University of Hong Kong]

Peering into the Halo of the Andromeda Galaxy Using Planetary Nebulae

Abstract

It has been widely accepted that in hierarchical cosmology, a large
galaxy evolves through accretion/merging of smaller galaxies. The
effects of such galaxy interaction are imprinted in the outer disk
or halo of a galaxy in the form of stellar condensations (i.e.,
substructures) like tidal streams. As the nearest large spiral
system, the Andromeda Galaxy (M31) is an excellent candidate to
study galaxy interaction and evolution. In order to study the halo
and substructures of M31 using planetary nebulae (PNe) as tracers
of chemistry and kinematics, we carried out very deep spectroscopic
observations of a carefully selected sample of PNe using the 10.4m
Gran Telescopio Canarias (GTC, La Palma). The target PNe are
located in different regions: the substructures (the Northern Spur
and the Giant Stream), the outer halo (or the exodisk) of M31, and
M32. Our chemical study reveals: 1) the halo PNe, as far as
~180 kpc from galactic center, have oxygen abundances close to the
solar value, supporting the current view that the external regions
of M31 are the result of complex interaction and merger process; and
2) the substructure PNe have lower oxygen abundances, indicating
a different origin.

77

2017-03-07 Tue14:20~15:20R1203

Quan-Zhi Ye[Caltech]

*Special Seminar*Aging comets and their meteor showers

Abstract

Active comets lost a significant amount of volatile every time they
pass through perihelion. As a result, comets will have less materials
for sublimation, and one would expect that comets will continue to fade
as they evolve. However, it is also suggested that the active lifetime
of a comet can consists of multiple active stages separated by temporary
dormant phases, making it difficult to identify true secular fading
caused by aging of comets. The era of modern astronomy is unfortunately
not long enough to cover the typical lifetime of a
comet (usually a few hundred orbits); however, comets produce dust
during their active stages, which are potentially detectable as meteor
activity at the Earth. Here I discuss the effort of understanding
cometary aging by examining different parts of the evolution spectrum of
Jupiter-family comets (JFCs), a group of comets that dominates the
cometary influx in the near-Earth space, using telescopic and meteor
observations as well as dynamical investigation.

78

2017-03-06 Mon14:20~15:20R1203

Paulo Freire[Max-Planck-Institut für Radioastronomie]

*Special Seminar*Testing the nature of gravitational waves with observations of binary pulsars

Abstract

In this talk, I will review some of the principles of pulsar timing, and review some of the results from the timing of binary pulsars from previous work. These include the observation of gravitational waves (GWs) in the energy loss of the "Hulse-Taylor" double neutron star, almost 40 years before the LIGO observation. I then introduce ongoing work, which tests the emission of GWs with far more accuracy than in the Hulse-Taylor pulsar, and new detections of the emission of gravitational waves in pulsar-white dwarf systems, which introduce strong constraints on the nature of GWs. In particular, we are able to exclude, within observing precision, any dipolar components of gravitational radiation, showing that they are almost purely quadrupolar. These results are then used for some of the most stringent tests of general relativity and alternative theories of gravity ever accomplished.

79

2017-03-01 Wed14:20~15:20R1203

Samantha Lawler[NRC Herzberg]

Does our Solar System Need to have Another Planet?

Abstract

The orbital element distribution of trans-Neptunian objects (TNOs) with large pericenters has been suggested to be influenced by the presence of an undetected, large planet at >200 AU from the Sun. To find additional observables caused by this scenario, we present here the first detailed emplacement simulation in the presence of a massive ninth planet on the distant Kuiper Belt. We perform 4 Gyr N-body simulations with the currently known solar system planetary architecture, plus a 10 M_earth planet with similar orbital parameters to those suggested by Trujillo & Sheppard or Batygin & Brown, and thousands of test particles in an initial planetesimal disk. We find that including a distant super-Earth-mass planet produces a substantially different orbital distribution for the scattering and detached TNOs, raising the pericenters and inclinations of moderate semimajor axis (50 < a < 500 au) objects. We test whether this signature is detectable via a simulator with the observational characteristics of four precisely characterized TNO surveys. We find that the qualitatively very distinct solar system models that include a ninth planet are essentially observationally indistinguishable from an outer solar system produced solely by the four giant planets. We also do not find any evidence for clustering of orbital angles in our simulated TNO population, and further simulations find that an additional planet causes significant changes in the orbits of known distant TNOs. Wide-field, deep surveys targeting inclined high-pericenter objects will be required to distinguish between these different scenarios.

The observation of molecular emission at millimetre and submillimetre wavelengths gives access to the study of stars having a large and cool circumstellar envelope as well as of the gas reservoirs of galaxies, in particular remote galaxies with redshift in the 2 to 5 range at the epoch of maximum star formation rate. The observation of the continuum emission underneath the molecular excitation lines provides important information on the dust content. Using Plateau de Bure and archival ALMA observations, we have been able to reconstruct in space, under simplifying hypotheses such as of invariance by rotation about an axis, both the morphology and the kinematics of such sources. Examples will illustrate these studies, including Asymptotic Giant Branch stars, protostars and gravitationally lensed high redshift galaxies.

81

2017-02-21 Tue14:20~15:20R1203

TBA[TBA]

*Special Seminar*

82

2017-02-15 Wed14:20~15:20R1203

Marc W. Buie[Southwest Research Institute]

Exploring the Outer Solar System with Occultations

Abstract

The Research and Education Collaborative Occultation Network (RECON) is a project to use occultations to probe basic properties of outer solar system objects. Occultation measurements can be done with relatively small telescopes but the principle challenge is in predicting events. RECON uses a strategy of a large set of fixed sites to overcome the prediction challenge. Our system uses 28-cm telescopes with high-sensitivity integrating video cameras hosted by schools across the Western United States. Our network consists of 56 stations with an average spacing of 50 km between stations. With this system, we reduce the prediction quality needed by an order of magnitude compared to a traditional “chase-the-shadow” deployment while also probing over a 2000 km region near the body. Such data can measure the sizes and shapes of the occulting body as well as detecting very close binary systems or rings and dust environments. RECON has ofetn been described as a citizen-science project but it is really more of a new collaborative research model. This presentation will review how the project was setup and is operated and provide examples of recent scientific results from our efforts.

83

2017-02-08 Wed14:20~15:20R1203

Peter Roelfsema[SRON]

A joint infrared space observatory - SPICA revised and upgraded

Abstract

The infrared wavelength domain allows measurements to directly assess the physical state and energy balance of cool matter in space, thus enabling the detailed study of the various processes that govern formation evolution of planets, stars and galaxies over cosmic time. Infrared space missions to date were hampered by either having a warm or a relatively small size telescope, limiting the practically achievable sensitivity. With SPICA we propose to take the next step in mid- and far-infrared research by combining a large, cold telescope with instruments employing modern ultra-sensitive detectors.
SPICA is to be launched in the late 2020s as a joint ESA-JAXA mission with instruments provided by Japanese and European consortia. The mission concept foresees a 2.5-meter diameter telescope cooled to below 8K, with the optical axis oriented perpendicularly to the axis of the spacecraft. Like on PLANCK, ‘V-grooves’ to provide passive cooling are combined with mechanical coolers to provide for an effective cryogenic system, as is needed for the cooling of the telescope assembly and the science instruments. With cooling not dependent on a cryogen the mission lifetime is expected to extend significantly beyond the required 3 years.
With the combination of low telescope background and instruments with state of the art detectors SPICA will provide spectroscopic capabilities at a uniquely high sensitivity of 2-5 x10-20 W/m2 (5σ/1hr). The instruments will offer resolutions ranging from R~50 through 3000 in the 17-230 μm domain as well as R~30.000 spectroscopy between 12 and 18 μm. Additionally the instruments will support efficient 17-35 μm broad band mapping, and small field spectroscopic imaging in the 35-230 μm range.
SPICA’s extreme spectroscopic sensitivity will give at least two orders of magnitude improvement over what has been attained to date. With this exceptional leap in performance new domains in infrared astronomy become accessible. For example, with this high sensitivity astronomers will be able to detect the [OIV] line in relatively average galaxies out to a redshift z~3. Thus, the evolution of galaxies can be followed through their most active periods in cosmic time from about 10 billion years ago to what they look like today. Also, we will be able to observe dust features from even earlier epochs, out to redshifts of z~7-8, thus providing insight into dust formation in the very early phases of the universe. Similarly, this new facility will allow us to study dust formation and evolution from very early epochs onwards, and to compare the formation history of planetary systems to that of our own solar system.

84

2017-01-18 Wed14:20~15:201F auditorium

Dominik Riechers[Cornell]

The Intricate Role of Cold Gas and Dust in Galaxy Evolution at Early Cosmic Epochs

Abstract

Dusty starburst galaxies at very high redshift represent an important
phase in the early evolution of massive galaxies. They typically
represent large-scale, gas-rich major mergers that trigger intense,
short-lived bursts of star formation, which consume most of the
available gas and drive the morphological transition to spheroids. At
early cosmic epochs, these hyper-luminous galaxies commonly trace
regions of high galaxy overdensity, and may be directly related to the
formation of galaxy clusters and their giant central
ellipticals. Molecular and atomic gas plays a central role in our
understanding of the nature of these often heavily obscured distant
systems. It represents the material that stars form out of, and its
mass, distribution, excitation, and dynamics provide crucial insight
into the physical processes that support the ongoing star formation
and stellar mass buildup. I will discuss the most recent progress in
studies of the cold gas content of dusty starburst galaxies at high
redshift, back to the first billion years of cosmic time using CARMA,
the Jansky Very Large Array, the Plateau de Bure interferometer, and
the Atacama Large (sub)Millimeter Array (ALMA). I will also highlight
our recent successful first detections of the interstellar medium in
"normal" (~L*) galaxies at z>5 with ALMA, and discuss the impact of
our findings on future studies back to even earlier epochs.

85

2017-01-11 Wed14:20~15:20R1203

Francesco Costagliola[Chalmers University of Technology]

Tracing the AGN/Starburst co-evolution in compact obscured nuclei

Abstract

Observations at all redshifts suggest that the AGN and starburst evolution across cosmic time are tightly linked. The recent discovery of ubiquitous giant molecular outflows revealed that even low-luminosity AGN can have a profound impact in the evolution and star-formation history of galaxies. The compact obscured nuclei of IR-luminous galaxies have been suggested to be the ideal targets to study the early stages of the Starburst/AGN interaction. However, because of the large extinction, standard Starburst/AGN tracers cannot be used to probe the central regions of these objects and new, more sensitive methods must be developed. Here I will report some of the latest results in the study of obscured AGN/Staburst activity including observations with ALMA and the JVLA.

Complex organic molecules (COMs) have been not only observed in hot cores of low- and high-mass protostars, but also were detected recently in cold dense clouds. Besides energetic processing of ices that were shown to produce organic species, it is interesting to understand COM formation also under dense cloud conditions, i.e., without the presence of embedded energy sources. We present our latest laboratory study of the low-temperature (15 K) solid state formation of three complex molecules – methyl formate (HC(O)OCH3), glycolaldehyde (HC(O)CH2OH) and ethylene glycol (H2C(OH)CH2OH) – through recombination of active intermediate radicals. These free radicals are formed via H-atom addition and abstraction reactions along the CO→H2CO→CH3OH hydrogenation network, which starts from CO gas accreted on the grain that successively reacts with H-atoms to form H2CO and CH3OH. The present work extends on a recent CO hydrogenation study and aims to resemble the physical-chemical conditions typical of dark molecular clouds. We confirm that H2CO, once formed by hydrogenation of CO, not only leads to CH3OH through forward addition reactions, but is also subject to backward abstractions induced by H-atoms, yielding CO again. In a similar way, H2CO is also the product of abstraction reactions of CH3OH. In this work, we show that the dominant intermediate radicals of CH3OH abstraction and H2CO addition reactions are CH2OH and CH3O, respectively. By considering both addition and abstration reactions, more reactive intermediates (HCO, CH3O and CH2OH) are produced in the ice mantle than previously thought, focussing on sequential H-atom addition reactions only. Inclusion of both types of reactions also enhances the probability to form COMs through radical-radical recombination without the need of UV photolysis or cosmic rays bombardment as external triggers. The formation of COMs realized in this way, is proven by RAIRS and TPD, also using isotopically labelled species.

87

2017-01-09 Mon14:20~15:20R1203

Erwin Lau[Yale]

*Special Seminar*Modeling baryonic physics in galaxy clusters

Abstract

Galaxy clusters play an important role in modern precision cosmology. As the most massive virialized objects in the universe, their abundance depends sensitively on cosmological parameters. However, uncertainties in galaxy cluster physics pose serious challenges to using forthcoming observations to make advances in cosmology with galaxy clusters.
In this talk, I will highlight how we can improve our understanding of galaxy cluster physics with the state-of-the-art numerical simulations and semi-analytical modelling. In particular, I will present results from the "Omega500" simulation, a high-resolution hydrodynamic simulation suite of galaxy cluster formation that follows the evolution of dark matter and baryons in a realistic cosmological setting. I will also outline upcoming challenges in the computational modelling of major physical processes in galaxy clusters, and how we can address them in anticipation of upcoming multi-wavelength cluster surveys in the next decade.

88

2017-01-04 Wed14:20~15:20R1203

Allison Man[ESO]

How to quench a massive galaxy?

Abstract

The progenitors of the local-day elliptical galaxies have formed the bulk of their stars in the first few Gyr of the Universe. This implies that already by z=2, there is a population of massive galaxies that have terminated their star formation somehow, and become quenched. Many plausible mechanisms have been proposed to explain early quenching in massive galaxies (e.g., active galactic nuclei feedback, halo quenching, morphological quenching). However, until recently the observations at hand are insufficient to allow us to distinguish between these mechanisms. I will review our knowledge on this topic thus far, and present efforts to tackle this decade-old question.